Photoelectric tube



May 4-, s, ASAO ET AL 2,079,477

PHOTOELECTR IC TUBE Filed Nov. 27, 1931 meta/ht su/phide coated with a/ka/i mater/2L Inventors: $oicl iro Asao mlyukl nagashirna, by Their At-L r n'eg.

Patented May 4, 1937 UNETED STATES PATENT (lFFl fiE PHOTOELECTREC TUBE Application November 27, 1931, Serial No. 577,650 In Japan December 30, 1930 6 Claims.

The present invention relates to photo-electric tubes, more especially to those tubes which contain cathodes coated with silver or similar metal and on which alkali material is deposited.

The object of the invention is to improve the light-sensitivity of tubes of this sort and the improvement is brought about by changing the usual treatment of the silver in forming the lightsensitive surface. Whereas it has been customary l heretofore to oxidize the silver prior to the deposition of the alkaline material thereon, we propose to convert the silver into the sulphide. The improvement has been found to result in tubes of considerably greater sensitivity than those here tofore fabricated.

In the manufacture of photoelectric tubes according to the prior art, silver is first vaporized as a thin film onto the support member which ordinarily comprises a portion of the glass bulb. The film is then oxidized by admitting oxygen into the bulb andheating or subjecting it to an electric discharge, after which alkali metal such as caesium or rubidium is evaporated or sputtered onto the oxidized surface. The bulb is then slightly heated to allow removal of the excess alkali metal by pumping. The light-sensitive material is believed to consist of a thin film or monatomic layer of alkali metal adsorbed on the oxidized silver. In accordance with the present invention, we propose to displace the oxidizing step referred to hereinbefore by a sulphurizing process, although as will be pointed out hereinafter, the improved step may be employed in addition to the usual oxidizing process. In either case, the use of sulphur has been found to produce marked increase in the sensitivity and performance of the tube.

The process of forming the sulphide may be carried out by admitting hydrogen sulphide or by introducing a lump of sulphur into the envelope in that part of the prior art process which ordinarily is occupied by the oxidation step. The 45 alkali metal adheres to the silver sulphide and the excess may be pumped out so as to leave a thin adsorbed alkali layer as in the case of the oxidized surface. While it is believed that in a tube, improved in accordance with our invention, the 50 light-sensitive material consists of a monatomic layer of alkali material on a base or foundation of silver sulphide, the light-sensitive material as a whole may exist in compound or mixture form of the various elements. Regardless of the exact 55 nature of the light-sensitive material, it is sufiicient to state that photo-electric tubes which have been treated with sulphur in vapor form are much more sensitive to an impinging light beam than are those which have been merely oxidized. While our invention is directed more especially 5 to the substitution of sulphur for the usual oxygen treatment, it also contemplates the use of sulphur in addition to oxygen.

In the drawing which exemplifies the invention, numeral 1 designates an evacuated envelope l0 and numeral 2 refers to the improved light-sensitive surface. This surface contains a window for the introduction of light. As stated hereinbefore, the various metals which are deposited on the envelope may be evaporated or sputtered 15 and for the purpose of evaporation, filaments of each material may conveniently be provided in the center of the bulb. One such filament is illustrated and designated by reference character 4. In order to prevent the material of the 20 filament from reaching the window which must be maintained transparent, a circular metal disk 5 is positioned between the filament and the window, said disk being mounted rigidly in a reentrant stem 8 which also supports the fila- 25 ment. There is illustrated a metal disk 1 positioned immediately above the reentrant stem, the function of the disk being to protect the stem from metal deposit.

It has been found further that the light- 30 responsive surface may be sensitized to an even greater degree by forming thereon a thin film of metal, such as cadmium or gold. These metals advantageously may be employed in connection with the sulphur treatment, with or without the use of oxygen. The gold may be readily applied to the light-sensitive surface by well known processes of vaporization or sputtering from a filament or other heated surface in substantially the same way as the silver is applied. The use of gold and similar metals for obtaining additional sensitization of alkali surfaces which have been previously oxidized, but not sulphurized, is disclosed and claimed in the patent application, Serial No. 539,383, Asao and Suzuki, filed May 22, 1931, entitled Photoelectric tubes and assigned to the same assignee as the present invention. This application has matured into Patent No. 1,936,419.

What We claim as new and desire to secure by Letters Patent of the United States, is:

1. A light-sensitive device comprising an envelope containing an electrode and a silver foundation metal on said envelope, a sulphur-containing coating on said foundation metal, and a layer of caesium on said coating.

2. A light-sensitive device comprising an envelope containing an electrode and a foundation metal on said envelope, a sulphur-containing coating on said foundation metal, a layer of alkali material on said coating, and a layer of gold on said alkali metal.

3. A light-sensitive tube comprising an envelope containing an electrode and a. layer of silver sulphide coated with alkali metal.

4. The process of fabricating a photo-electric tube which comprises depositing a foundation metal on the interior of the tube, introducing a sulphide into the tube whereby the foundation metal is converted into a metallic sulphide, de-

positing on the sulphide a layer of light-sensitive material and coating said material with gold.

5. A light-sensitive device consisting of an envelope containing an electrode, and a lightsensitive coating on said envelope, said coating including a noble metal and sulphur with a superposed layer of alkali material.

6. A light-sensitive device comprising an envelope containing an electrode and a foundation metal on said envelope, a sulphur-containing coating on said foundation metal, a layer of alkali metal on said coating and a layer of cadmium on said alkali metal.

SOICHIRO ASAO. MIYUKI NAGASHIMA. 

